Transcript Electrical Systems

Automotive Electrical Systems
R. Bortignon
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Electrical System Service & Testing…
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Testing Fuses
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1) test with an ohmmeter set on the low scale
 should have low/no resistance
 be careful checking fuses visually
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Testing Fuses
2) test with a test light
 the key may have to be in the on position
 the control/switch for the circuit may have to be on
test light should light up on both sides of the fuse
if only one side lights up – fuse is open
if neither side lights up – power is not reaching the fuse
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Relays
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use a low current signal to activate a high current circuit
relay coil draws 150mA
contacts can conduct 30-50amps
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Electrical Faults – High Resistance
• circuit may not work at all
• circuit may be dim or work poorly / slowly
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Electrical Faults – Low Resistance
 the load’s resistance is partially or totally bypassed
 often referred to as a short
 causes higher than normal current flow
 usually causes fuse to open the circuit
frayed wire/bare insulation
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Light Bulbs
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bulbs can be single or double filament
 double filament = brake light & park light
 note the offset indexing pins & 2 contacts
 newer style bulbs do not require indexing
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Testing Bulbs
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often “blown” bulbs are easily seen during a visual inspection
sometimes a DVOM will verify the problem
 use low resistance setting
 polarity doesn’t matter
 most bulbs will be ≈ 3Ω to 10Ω
 you are looking for…
 shorts (low/no Ω)
 opens (high Ω)
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Testing Headlamps
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older style sealed beams
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newer halogen, xenon bulbs
 do not touch the quartz when replacing these!
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1 connector is for ground – check for continuity to ground
2nd connector is for hi beam – check for voltage
3rd connector is low beam – check for voltage
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Turn Signals
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blinking function of the turn signals is controlled by turn signal flasher
may have 1 that controls turn signals & 4 way flasher
or 2 separate units
located in fuse box or under the left side of the dash
 if one side flashes abnormally fast – check for faulty bulb on that side of the vehicle
 if both sides flash incorrectly, the flasher unit may be faulty
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Reading Wiring Diagrams
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wire colors – jacket color followed by stripe color
connectors – identification numbers
usually + side of the circuit up top & ground at the bottom
ground number & locations
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Using Component Location Function
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component locator can be used to find connectors, relays, grounds, modules etc.
access electrical, then component location in Mitchell
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Starter Circuit
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terminal “B” (battery) is live at all times
terminal “S” (start) feeds power only when the key is in the starting position
 “S” terminal will have a neutral safety switch in series for an automatic transmission equipped
car
 “S” terminal can also have a clutch safety switch in series for a manual transmission equipped car
 “S” terminal may have remote starter switch or alarm disabling feature tied into it
terminal “M” (motor) has power during cranking only
M
B
S
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Starter Solenoid
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serves same purpose as a relay
is usually mounted directly on the starter motor
on Fords, it is mounted remotely on the inner fender
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Voltage Drop Test
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determines if too much voltage is being lost to poor connections
voltmeter is set to low voltage scale (0-2v)
meter leads are placed across a connection (circuit must be turned on during testing)
there should not be more than .1v loss per connection
both the positive and ground circuits can be tested this way
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Hey Mr. B can I install…
• the next 5 slides are helpful when adding electrical accessories to a vehicle
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Adding Accessories
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you and your students need to carefully consider what’s needed when adding amplifiers,
driving lights etc.
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add a relay to an existing circuit so you don’t overload the original circuit
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Adding Fuses to Add-on Accessories
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when adding additional equipment, add a relay to power the circuit
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calculate the required fuse amperage
 eg: 2 fog lights 4Ω each
 amperage = 12 volts ÷ 4Ω = 3 amps through each light
 3 amps X 2 lights = 6 amps total
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6 amps flowing through circuit
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multiply this by 1.5 to allow for any voltage surges
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6 amps X 1.5 = install a 9 amp fuse
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Hey Mr. B, do you have any wire?
determining wire gauge size for add-on circuits…
 use a wire gauge table
 always better to use a larger gauge size than is required
3'
5'
7'
10'
15'
20'
25'
up to 5 amps
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Wiring Repair Tips
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use grommets & loom to protect wires against abrasion
crimp & solder, then heat shrink
don’t rely on crimp only
on air bag systems & circuits to/from computer modules, follow manufacturer’s specific
repair instructions
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ISO 4 pin & 5 pin relay pin-outs
…for your reference
4 pin relay
5 pin relay
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Additional Resources
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from the 5050 ShareOut, download the electrical PDF file for your reference
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4 short videos have been placed on the 5050 ShareOut folder…
 voltage drop
 electrical faults
 measuring current flow
 reading wiring diagrams
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